1. Field of the Invention
The present invention relates to a machine tool for carrying out at least turning operations, which comprises a first headstock for holding a workpiece and a second headstock, which is disposed in confronting relation to the first headstock, for holding a workpiece.
2. Description of the Related Art
Japanese published patent application No. 5-57506 discloses a machining center for machining bars. The disclosed machining center has a rotating table (corresponding to a first headstock according to the present invention) for gripping a workpiece and another rotating table (corresponding to a second headstock according to the present invention), which is disposed in confronting relation to the first-mentioned rotating table, for gripping a workpiece.
Japanese published patent application No. 7-88702 discloses a method of supplying a workpiece to and ejecting the workpiece from a lathe. According to the disclosed method, a pair of robot hands is disposed one on each side of a hand bracket, and change workpieces on a headstock of the lathe.
In the machining center disclosed in Japanese published patent application No. 5-57506, the other rotating table swivels in a horizontal plane. Japanese published patent application No. 5-57506 is silent as to any way of ejecting a machined workpiece smoothly out of the machining center without causing damage to the workpiece.
According to the method disclosed in Japanese published patent application No. 7-88702, the robot hands grip the workpiece and transfer the workpiece to and from the headstock of the lathe. The lathe itself needs to have a device for supplying and ejecting the workpiece.
General machine tools for performing turning operations according to the related art are mostly devoid of a workpiece changer. When such a machine tool has machined a workpiece, the machine tool stops its machining process and waits for the operator to attend the machine tool. Upon arrival at the machine tool, the operator removes the machined workpiece from the machine tool, and supplies a non-machined workpiece to the machine tool. Thereafter, the machine tool resumes its machining process on the non-machined workpiece which is mounted on its headstock.
Since the general machine tools according to the related art need to stop their machining process for changing workpieces, the utilization ratio of the machine tools tends to be lowered. In addition, it is burdensome for the operator to change the workpieces on the machine tools.